1. Field of the Invention
The present invention relates to an electrolytic capacitor excellent in heat dissipation performance for use in electronics devices and other devices. In this disclosure, language “Aluminum” denotes aluminum and its alloy.
2. Description of the Related Art
The following description sets forth the inventor's knowledge of related art and problems therein and should not be construed as an admission of knowledge in the prior art.
In most electrolytic capacitors, a capacitor element is accommodated in a cylindrical external casing having a bottom, and electrode terminals are connected to the capacitor element. In such electrolytic capacitors, when ripple current is applied for a long time period or intense current is applied, the capacitor element accommodated therein generates heat. Furthermore, as the size of an electrolytic capacitor increases, the calorific value of the capacitor element further increases. Excessively increased temperature of the capacitor elements due to the heat generation causes deteriorated electrical characteristics of the capacitor such as increased dielectric dissipation factor or decreased capacitance, and also shortens the useful life of the capacitor.
To solve the aforementioned problems, conventionally, an electrolytic capacitor capable of restraining the temperature rise of the capacitor element has been proposed.
For example, an electrolytic capacitor in which metallic collector electrodes are connected to end surfaces of its capacitor element has been proposed (see Japanese Unexamined Laid-open Patent Publication No. P2000-77268 (hereinafter “Patent Document 1”), claim 1). Another electrolytic capacitor also has been proposed. In this electrolytic capacitor, a heat absorbing portion of a heat pipe is disposed in the core portion of the capacitor element, and a heat releasing fin or a heat sink is attached to the heat releasing portion of the heat pipe disposed outside the capacitor (see Japanese Unexamined Laid-open Patent Publication No. H11-329899 (hereinafter “Patent Document 2”), claim 1 and FIG. 1, Japanese Unexamined Laid-open Patent Publication No. H11-176697 (hereinafter “Patent Document 3”), claims 1 and 2, FIG. 1).
In an electrolytic capacitor in which a capacitor element is accommodated in a cylindrical external casing having a bottom, it is also known that silicon oil is filled in a gap between the external casing and the capacitor element to improve the heat dissipation performance (see Japanese Unexamined Laid-open Patent Publication No. P2002-110479 (hereinafter “Patent Document 4”), claim 1).
However, in the aforementioned electrolytic capacitors disclosed in the aforementioned Patent Documents 1 to 3, it is required to manufacture an electrolytic capacitor having a capacitor element and/or an inner structure different from that of a conventional electrolytic capacitor, which results in increased manufacturing cost.
In general, as an external casing, a synthetic resin (polymer) casing or a metallic casing is used (see paragraph number of [0018] of Patent Document 1). However, in cases where the synthetic resin casing is employed, the synthetic resin casing disturbs the heat dissipation because of the poor heat conductivity. On the other hand, in cases where the metallic casing is employed, a synthetic resin sleeve 101 is generally provided outside the metallic casing 100 to establish heat insulation as shown in FIG. 3 (see Patent Document 4). In this case, however, the heat dissipation is also disturbed by the thin air layer (heat insulation layer) formed between the metallic casing 100 and the synthetic resin sleeve 101.
In the electrolytic capacitor disclosed in the aforementioned patent document 4, no change in design of the capacitor element and/or the inner structure is required. In this sense, it is preferable, but the heat dissipation was not satisfactory. Especially, in recent years, as electrolytic capacitors for inverter circuits or AC servomotor driving circuits for use in, e.g., electric automobiles, fuel-cell vehicles, solar energy generation systems or industrial power sources, it has been required to provide an electrolytic capacitor which is excellent in heat dissipation and capable of efficiently radiating heat generated at the time of impressing heavy current or high ripple current. The technique disclosed in the aforementioned patent document 4 could not meet such a demand.
The description herein of advantages and disadvantages of various features, embodiments, methods, and apparatus disclosed in other publications is in no way intended to limit the present invention. Indeed, certain features of the invention may be capable of overcoming certain disadvantages, while still retaining some or all of the features, embodiments, methods, and apparatus disclosed therein.